US7302845B2 - Method for measurement of gas flow velocity, method for energy conversion using gas flow over solid material, and device therefor - Google Patents

Method for measurement of gas flow velocity, method for energy conversion using gas flow over solid material, and device therefor Download PDF

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US7302845B2
US7302845B2 US10/544,244 US54424405A US7302845B2 US 7302845 B2 US7302845 B2 US 7302845B2 US 54424405 A US54424405 A US 54424405A US 7302845 B2 US7302845 B2 US 7302845B2
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gas
gas flow
flow
electrical energy
sensing device
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US20060191353A1 (en
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Ajay Kumar Sood
Shankar Ghosh
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MS Indian Inatitute of Science
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects
    • G01F1/20—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by detection of dynamic effects of the flow
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/56—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects
    • G01F1/64—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using electric or magnetic effects by measuring electrical currents passing through the fluid flow; measuring electrical potential generated by the fluid flow, e.g. by electrochemical, contact or friction effects
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
    • G01F1/688—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
    • H02N11/00—Generators or motors not provided for elsewhere; Alleged perpetua mobilia obtained by electric or magnetic means
    • H02N11/002—Generators
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites

Definitions

  • the present invention relates to a method for energy conversion by gas flow over solid materials. More particularly, the present invention relates to a method for the generation of voltage and current by gas flow over solid material such as doped semiconductors, graphite, and the like. In particular, the present invention also relates to a method for the conversion of energy by a gas flow over a solid material using a combination of the Seebeck effect and Bernoulli's principle. The present invention also relates to a method for the measurement of velocity of a gas along the flow thereof as a function of the electricity generated in the solid material due to the flow of the gas along the surface thereof.
  • the measurement of gas velocity along the direction of flow is of significant importance in several applications. For example, an accurate determination of wind velocity over oceans or rivers along the direction of the flow is important in predicting tidal patterns, potential weather fluctuations, etc.
  • the measurement of wind velocity is also of importance in aeronautics such as in wind tunnels to determine the aerodynamics of aircraft designs. Another area where determination of wind velocity is of importance is in airports wherein an accurate determination of wind velocity will increase the safety factor in the landing and take off of airplanes. Another area where determination of wind velocity is of importance is in the field of disaster management. The accurate determination of wind velocity is useful for determining the potential for natural disasters like typhoons, tornadoes and avalanches.
  • one method of low speed flow field velocity determination comprises particle imaging velocimetry, which comprises suspending aerosol particles in the gas.
  • a fast charge coupled device is provided across the planar cross section of the flow in order to image the colloidal particles.
  • the small seed colloidal particles are illuminated using a laser light sheet.
  • the charge coupled device camera electronically records the light scattered from the particles. Analysis of the image obtained enables determination of the particle separation, and thereby the velocity of the particles, which are assumed to follow the path of the flow.
  • the primary disadvantage is the underlying assumption that the movement of all the colloidal particles assume the direction of the flow. This is not necessarily true in the case of large sized particles or in the case of ver low velocities. Thus, the application of this method is limited to velocities of greater than 2 cm/s. It is thus, also important in this method, to ensure that the particle size is small enough to ensure that the particle follows the flow of the gas but at the same time is large enough to effectively scatter light. The equipment required (lasers, CCD cameras) is also large in size. Another disadvantage is that the method is dependant entirely on image analysis and thereby on the analysis algorithms.
  • the particle imaging velocimetry method measures the velocity of the colloidal particles and there is no direct digital signal corresponding to the gas velocity; the flow velocity of pure gas cannot be measured.
  • the method also is not appropriate for systems where optical access is absent.
  • Another disadvantage is that the equipment required such as lasers and charge coupled devices are expensive.
  • Doppler velocimetry comprises measurement of the Doppler shift of scattered light from the gas.
  • the method relies on the fluctuation in the intensity of scattered light received from a gas when passing through the intersection of two laser beams.
  • the Doppler shift between the incident and the scattered light is equal to the frequency of the fluctuation of intensity which is therefore proportional to the component of gas velocity lying in the plane of the two laser beams and perpendicular to their bisector.
  • This method also suffers from several disadvantages.
  • the method is operable where the particle velocities are greater than 0.1 cm/sec. This method also requires large and expensive equipment such as a plurality of lasers and digital counters.
  • Another significant disadvantage of this method is that it is restricted to a single point measurement. Similar to particle imaging velocimetry, this method also requires that the particle size be small enough to flow along the gas flow path easily but large enough to produce the required signal above the noise threshold. This method also does not work in systems where optical access to the gas flow path at the measurement volume is absent. Signal level depends on the detector solid angle. As a result while the Mie scattering intensity is substantially better in the forward direction, it is difficult to set up forward receiving optics which remain aligned to the moving measurement volume. Greater noise at higher speed with radio frequency interference is possible. Again, similar to the PIV method, the flow velocity of unseeded gas cannot be measured since there is no direct digital signal corresponding to the gas velocity. This method is appropriate only for gas containing colloidal particles and not for clear gas.
  • U.S. Pat. Nos. 3,915,572 and 6,141,086 disclose a Laser Doppler velocimeter for measurement of velocity of objects or wind so as to determine the speed or relative speed of the object (such as for example an automobile) or in the case of wind measurement, the true air speed or wind gradients such as wind shear.
  • Another known method to measure fluid velocity comprises the measurement of heat transfer change using a electrically heated sensor such as a wire or a thin film maintained at a constant predetermined temperature using an electronic control circuit.
  • the heat sensor is exposed to the fluid whose velocity measurement is to be taken.
  • the fluid flowing past the sensor cools the heat sensor which is compensated by an increased current flow from the electronic control circuit.
  • the flow velocity of the fluid can be measured as a function of the compensating current imparted to the heater by the electronic control circuit.
  • the sensor generally is operable at fluid velocities of greater than 1 cm/second and not for very low velocities. At low velocities, the convention currents in the gas cause a malfunction in the sensor.
  • U.S. Pat. No. 6,470,471 discloses a gas flow sensor using a heated resistance wire commonly called a hot wire anemometer.
  • U.S. Pat. No. 6,112,591 discloses a high response, heat transfer detection type flow sensor manufactured using micro-machining technology for IC production. This sensor has an improved efficiency of heat transfer from a heating element to heat receiving (sensing) element by controlling the direction of the gas flow between the elements or by using the characteristics of the fluid flow therein.
  • Yet another method for the measurement of flow velocities comprises the use of rotary flour meters which work on an arrangement of turbine wheels.
  • the motion of the gas through the turbine otherwise called the rotor wheel, causes the turbine to rotate.
  • the rotational frequency of the rotor wheel depends on the velocity of the gas and is measured using either an electro-optical system or by electronically sensing the square wave pulse generated by magnets embedded in the turbine vanes.
  • the size of the sensor arrangement is also to the order of 50 cm 3 .
  • the rotary flow meter is suitable for use in cooling systems irrespective of the nature of the gas (clear or seeded) and the sensor can determine if the gas is flowing in the forward or reverse direction.
  • the main object of the invention is to provide a method for the determination of flow velocity of a gas along the direction of the flow as a function of the electricity generated due to the flow of the gas across a solid material.
  • Another object of the invention is to provide a method for the generation of electricity without reliance on any nuclear, thermal or hydroelectric power source and based purely on the flow of a gas.
  • a further object of the invention is to provide a flow sensor device that does not require any external source of power for its operation.
  • a further object of the invention is to provide an energy conversion device that does not require any external source of power for its operation.
  • the present invention provides a method for the determination of gas flow velocities irrespective of the nature of the gas or the flow velocity thereof, which comprises positioning a flow sensing device in a gas flow, said flow sensing device comprising of at least one electrically conducting solid material positioned at an angle to the gas flow, at least one conducting element connecting said at least one conducting material to a electricity measurement means, the gas flow over said at least one solid material generating a flow of electricity along the direction of the gas flow due to the pressure gradient developed across the solid material, said electrical energy being transmitted by said conducting element to said electricity measurement means provided external to the gas flow, to measure the electricity generated as a function of the rate of flow of said flow.
  • the solid material comprises a material with a high Seebeck coefficient.
  • the solid material is selected from the group consisting of doped semiconductor, graphite, single wall type carbon nanotube, multi-wall type carbon nanotube, and metallic material with a high Seebeck coefficient.
  • the doped semiconducting material is selected from the group consisting of n-Germanium, p-Germanium, n-silicon and p-silicon.
  • the metallic material is selected from polycrystalline copper, GaAs, Tellurium and Selenium.
  • the gas is selected from the group consisting of nitrogen, argon, oxygen, carbon dioxide and air.
  • the response time of the flow sensing device is less than 0.1 second.
  • the induced voltage in the solid material due to the flow of the gas depends on a temperature difference across the solid material along the direction of inviscid flow.
  • gas velocity is in range of 1 to 140 m/s.
  • the gas flow across the solid material is at an angle in the range of 20° to 70°, preferably 45°.
  • the present invention also provides a flow sensing device useful for measurement of gas flow velocities irrespective of the flow velocity or the nature of the gas, said device comprising at least one gas flow sensing element and at least a conducting element connecting said solid material to a electricity measurement means.
  • the gas flow sensing element comprises a solid material with good electrical conductivity and high Seebeck coefficient.
  • the solid material is selected from the group consisting of doped semiconductor, graphite, single wall type carbon nanotube, multi-wall type carbon nanotube, and metallic material with high Seebeck coefficient.
  • the doped semiconducting material is selected from n-Germanium, p-Germanium, n-silicon and p-silicon.
  • the metallic material is selected from polycrystalline copper, GaAs, Tellurium and Selenium.
  • the gas is selected from the group consisting of nitrogen, argon, oxygen, carbon dioxide and air.
  • the electricity measurement means comprises a ammeter to measure the current generated across the opposite ends of said at least one or more solid material or a voltmeter to measure the potential difference across the two opposite ends of the said one or more solid material.
  • the flow sensing device comprises of a plurality of doped semiconductors all connected in series or parallel with a single conducting element each being provided at the respective extreme ends of the said plurality of doped semiconductors.
  • the said plurality of doped semiconductors are connected in series so as to measure the potential difference generated across the ends of the said plurality of doped semiconductors.
  • the said plurality of doped semiconductors are connected in parallel to each other so as to enable determination of the current generated across the two ohmic contacts formed by the respective conducting elements at the ends thereof.
  • the gas flow sensor comprises of a matrix consisting of a plurality of gas flow sensing elements consisting of solid materials connected by metal wires, the entire matrix being provided on a high resistance undoped semiconducting base, said semiconducting base being connected to a electricity measurement means.
  • the electricity measurement means is selected from a voltmeter and an ammeter.
  • the gas flow sensing elements forming the matrix and the metal wires connecting said gas flow sensing elements are provided on a single hip.
  • the gas flow sensor comprises of alternate strips of n and p type semiconductors, each n and p type semiconductor strip being separated from its immediate neighbor by an thin intervening layer of undoped semiconductor, said alternate strips of n and p type semiconductors being connected by a conducting strip, said alternate strips of n and p type semiconductors with intervening undoped semiconductor layers, and conducting strip being provided on a semiconducting base material, electrical contacts being provided at two opposite ends of the base material and connected to a electricity measurement means.
  • the flow sensing device comprises of a plurality of carbon nanotubes all connected in series or parallel with one conducting element each being provided at respective extreme ends of plurality of carbon nanotubes.
  • the said plurality of carbon nanotubes are connected in series so as to measure the potential difference generated across the ends of the said plurality of carbon nanotubes.
  • the said plurality of nanotubes are connected in parallel to each other so as to enable determination of the current generated across the two ohmic contacts formed by respective conducting elements at ends thereof.
  • the flow sensing device is provided on a insulated base.
  • the conducting element comprises of a wire.
  • the conducting element comprises an electrode.
  • the conducting element comprises of a combination of a wire connected to an electrode.
  • the invention also relates to method for the generation of electrical energy using an energy conversion device comprising at least one energy conversion means, at least a conducting element connecting said energy conversion means to a electricity storage or usage means, the flow of a gas across the energy conversion means resulting in is generation of a Seebeck voltage being generated in each energy conversion means along the direction of the gas-flow, thereby generating electrical energy, said electrical energy being transmitted to the energy storage or usage means through the conducting elements.
  • the energy conversion means comprises a solid material with good electrical conductivity and high Seebeck coefficient.
  • the solid material is selected from the group consisting of doped semiconductor, graphite, a single wall type carbon nanotube, a multi-wall type carbon nanotube, and metallic material with a high Seebeck coefficient.
  • the doped semiconducting material is selected from group consisting of n-Germanium, p-Germanium, n-silicon and p-silicon.
  • the metallic material is selected from polycrystalline copper, GaAs, Tellurium and Selenium.
  • the gas is selected from the group consisting of nitrogen, argon, oxygen, carbon dioxide and air.
  • the flow sensing device comprises of a plurality of doped semiconductors all connected in series or parallel with a single conducting element each being provided at the respective extreme ends of the said plurality of doped semiconductors.
  • the said plurality of doped semiconductors are connected in series.
  • the said plurality of doped semiconductors are connected in parallel.
  • the energy conversion device comprises of a matrix consisting of a plurality of gas flow sensing elements consisting of solid materials connected by metal wires, the entire mat being provided on a high resistance undoped semiconducting base, said semiconducting base being connected to a electricity storage or usage means.
  • the gas flow sensing elements forming the matrix and the metal wires connecting said gas flow sensing elements are provided on a single chip.
  • the energy conversion device comprises of alternate strips of n and p type semiconductors, each n and p type semiconductor strip being separated from its immediate neighbor by an thin intervening layer of undoped semiconductor, said alternate strips of n and p type semiconductors being connected by a conducting strip, said alternate strips of n and p type semiconductors with intervening undoped semiconductor layers, and conducting strip being provided on a semiconducting base material, electrical contacts being provided at two opposite ends of the base material and connected to a electricity storage or usage means.
  • the energy conversion device comprises of a plurality of carbon nanotubes all connected in series or parallel with a single conducting element each being provided at the respective extreme ends of the said plurality of carbon nanotubes.
  • the said plurality of carbon nanotubes are connected in series.
  • the said plurality of nanotubes are connected in parallel.
  • the energy conversion device is provided on an insulated base.
  • the conducting element comprises of a wire.
  • the conducting element comprises of an electrode.
  • the conducting element comprises of a combination of a wire connected to an electrode.
  • the energy storage means comprises of a battery or storage cell.
  • the response time of the flow sensing device is less than 0.1 second.
  • the induced voltage in the solid material due to the flow of the gas depends on a temperature difference across the solid material along the direction of inviscid flow.
  • the gas velocity is in the range of 1 to 140 m/s.
  • the gas flow across the solid material is at an angle in the range of 20° and 70°, preferably 45°.
  • the invention also relates to an energy conversion device comprising a energy generation means comprising one or more energy conversion means, each said one or more energy conversion means comprising of at least one solid material with a high Seebeck coefficient, at least one conducting element connecting said at least one energy conversion means to a electricity storage or usage means to store or use the electricity generated in the said one or more energy conversion means due to a gas flow across the energy conversion means.
  • the solid material is selected from the group consisting of a doped semiconductor, graphite, a single wall type carbon nanotube, a multi-wall type carbon nanotube, and metallic material with a high Seebeck coefficient.
  • the doped semiconducting material is selected from the group consisting of n-Germanium, p-Germanium, n-silicon and p-silicon.
  • the metallic material is selected from polycrystalline copper, GaAs, Tellurium and Selenium.
  • the gas is selected from the group consisting of nitrogen, argon, oxygen, carbon dioxide and air.
  • a electricity measurement means is provided connected to the one or more energy conversion means through said conducting element, comprising an ammeter to measure the current generated across the opposite ends of said at least one or more solid material or a voltmeter to measure the potential difference across the two opposite ends of the said one or more solid material.
  • the energy conversion means comprises of a plurality of doped semiconductors all connected in series or parallel with a single conducting element each being provided at the respective extreme ends of the said plurality of doped semiconductors.
  • the said plurality of doped semiconductors are connected in series.
  • the said plurality of doped semiconductors are connected in parallel.
  • the energy conversion device comprises of a matrix consisting of a plurality of energy conversion means consisting of solid materials connected by metal wires, the entire matrix being provided on a high resistance undoped semiconducting base, said semiconducting base being connected to a electricity storage or usage means.
  • the energy conversion means forming the matrix and the metal wires connecting said energy conversion means are provided on a single chip.
  • the energy conversion means comprises of alternate strips of n and p type semiconductors, each n and p type semiconductor strip being separated from its immediate neighbor by an thin intervening layer of undoped semiconductor, said alternate strips of n and p type semiconductors being connected by a conducting strip, said alternate strips of n and p type semiconductors with intervening undoped semiconductor layers, and conducting strip being provided on a semiconducting base material, electrical contacts being provided at two opposite ends of the base material and connected to a electricity storage or usage means.
  • the energy conversion means comprises of a plurality of carbon nanotubes all connected in series or parallel with a single conducting element each being provided at the respective extreme ends of the said plurality of carbon nanotubes.
  • the said plurality of carbon nanotubes are connected in series.
  • the said plurality of nanotubes are connected in parallel.
  • the energy conversion device is provided on an insulated base.
  • the conducting element comprises of a wire.
  • the conducting element comprises of an electrode.
  • the conducting element comprises of a combination of a wire connected to an electrode.
  • the electricity storage means is a battery.
  • FIG. 1( a ) is a schematic representation of the flow sensing device used in the method of the invention.
  • FIG. 1( b ) is a schematic representation of the flow sensing device of the invention wherein the conducting elements are dearly displayed and depicting an angle of 45° to the horizontal axis of the gas flow. Angles between 20° and 70° can also be used.
  • FIG. 1( c ) is a graph of the typical response of the response obtained by a device wherein the flow sensing element was an n doped Ge in a flow of argon gas at a flow velocity of 7 m/s.
  • FIG. 1( d ) is another schematic representation of the device of the invention wherein an experimental set up is provided to achieve a calibrated gas flow velocity (u) on the flow sensor.
  • FIG. 2 is a graph showing the dependence of the signal V on the flow velocity of nitrogen for (bottom to top) n-Si (filled up triangles), n-Ge (stars), graphite (open squares), Pt metal (plus), SWNT (open circles), MWNT (open triangles) and p-Si (filled triangles).
  • the inset in FIG. 2 shows the dependence of V for n-Ge as a function of the active length d for a fixed value of velocity (u).
  • FIG. 4 is a graph of V versus M 2 for the flow of argon (filled squares) and nitrogen (open circles). The inset shows the expanded plot of regime I.
  • FIG. 5 is a schematic of the device according to one embodiment of the invention showing various gas flow sensor elements connected by means of metallic wires in a matrix formation and provided on a high resistance and undoped semiconductor substrate.
  • FIG. 6 is a schematic of another embodiment of the device of the invention showing alternate strips of n and p type semiconducting material with interposed layers of undoped semiconducting material, the alternating n and p type semiconducting material being connected by means of a conducting strip, the entire assembly being provided on a semiconducting base provided with two electrical contacts for connection to a electricity storage or electricity measurement means.
  • the present invention therefore provides a method and device for the generation of electricity due to the flow of different types of gases such as nitrogen, argon, oxygen air and the like over/across a variety of solid materials.
  • the solid materials are substantially good conductors of electricity and can be selected from materials such as metallic materials, semiconductors, graphite, nanotubes and the like. The primary requirement is that such materials have a good Seebeck coefficient.
  • All embodiments of the present invention are based on the induction of electrical energy in a solid material due to the flow of a gas across the solid material thereby generating a Seebeck voltage in the solid material. This is irrespective of the velocity of the gas flow or the nature of the gas such as the purity or turbidity thereof, the volume of flow thereof at the measurement point, or any variations in external parameters such as pressure or density.
  • FIG. 1( a ) is a schematic representation of the device used for flow measurement of gas velocity according to the method of the invention.
  • a single flow sensing element such as a n doped Ge semiconductor ( 1 ) is shown sandwiched between two metal electrodes ( 2 , 2 ′) provided at each end thereof.
  • the metal electrodes ( 2 , 2 ′) form ohmic contacts for the semiconductor ( 1 ).
  • the combination of the semiconductor ( 1 ) and the metal electrodes ( 2 , 2 ′) provided thereon are supported on an insulating material base (not shown) made for example of undoped semiconducting material or of any insulating material such as polytetrafluoroethylene.
  • the insulating base with the semiconductor ( 1 ) and electrodes ( 2 , 2 ′) are immersed at an angle of 45° to the horizontal axis of the gas flow ( 3 ) whose velocity is to be measured.
  • the gas flow is through a tube ( 4 ).
  • the tube can be used to pass different gases at different velocities.
  • the electrodes ( 2 , 2 ′) are connected to an electricity measurement means ( 5 ) such as a voltmeter through lead wires ( 6 , 6 ′).
  • the voltage measurement means ( 5 ) is provided external to the tube ( 4 ).
  • the direction of the flow of the gas in FIG. 1( a ) is depicted by the arrow through the tube ( 4 ) which continues over the flow sensing element ( 1 ).
  • FIG. 1( b ) is a schematic representation of the flow sensing device of the invention wherein the conducting elements are clearly displayed and depicting the angle of 45° to the horizontal axis of the gas flow. Other angles between 20° and 70° can also be used.
  • the flow sensing element ( 1 ) is sandwiched between two electrodes ( 2 , 2 ′ which are in turn connected to the respective terminals of a electricity measurement means ( 3 ) through leads ( 4 ).
  • the direction of the accelerating flow of the gas is depicted by the continuous arrow.
  • d represents the active portion of the device which is at an angle of 45° to the horizontal axis of the flow direction.
  • the schematic of FIG. 1( b ) was used in example 3 below, wherein the specific construction and results obtained will be explained.
  • FIG. 1( c ) is a graphical representation of the typical response obtained when the device of FIG. 1( b ) is used wherein n doped Ge is the flow sensing element.
  • FIG. 1( d ) is a schematic representation of one embodiment of the device of the invention used to achieve a calibrated gas flow velocity on the solid material of the device.
  • the device of the invention comprises a flow sensing element ( 1 ) connected at either end thereof to two respective conducting elements ( 2 ), said conducting elements being connected in turn to the positive and negative terminals of a electricity measurement means such as a voltmeter ( 3 ).
  • the flow sensing element ( 1 ) is kept at an angle of 45° to the horizontal axis of the gas flow from a gas source ( 4 ) such as a compressed gas cylinder through a tube ( 5 ).
  • the flow rate at the exit point of the tube ( 5 ) is measured deduced from the measured flow rate at a side port ( 6 ) provided in the tube ( 5 ) using a rotameter ( 7 ).
  • the present invention shows for the first time that there is a direct generation of voltage due to the flow of gases such as argon, nitrogen and oxygen over solid material such as doped semiconducting material, graphite, single wall carbon nanotube, multiwall carbon nanotube and the like which have a high Seebeck coefficient.
  • gases such as argon, nitrogen and oxygen over solid material
  • solid material such as doped semiconducting material, graphite, single wall carbon nanotube, multiwall carbon nanotube and the like which have a high Seebeck coefficient.
  • the gas velocities utilized were in the range of 1 to 140 m/s.
  • the present invention also demonstrates that voltage and current depend quadratically on the flow velocity and the magnitude and sign of the voltage depends on the properties of the solid material. For example, argon at a flow velocity of 11 m/s generated a voltage of ⁇ 16.4 ⁇ L for n-type Ge but a voltage of 5.9 ⁇ V for single wall carbon nanotube.
  • the present invention also demonstrates that a sensor to measure the flow velocity of the gases can be made based on the generated electrical signal.
  • the sensor of the invention is an active sensor which gives direct electrical response to the gas flow. This should be compared with the widely used gas flow sensor based on thermal anemometry, wherein, the fluid velocity is sensed by measuring changes in heat transfer from a small, electrically-heated sensor (wire or thin film) exposed to the fluid. Thermal anemometry works on heat balance equations and hence any small change in the temperature, pressure or composition of the gas can cause erroneous readings. Such effects are absent or are minimal in the case of the present invention and can, even if present, be taken into account in the sensors based on the direct generation of gas flow-induced voltage or current in the sensor material.
  • FIG. 5 of the accompanying drawings a number of gas flow sensing elements ( 51 , 51 ′, 51 ′′, . . . ) are interconnected in the form of a matrix using metal wires ( 52 ). The entire matrix is developed on a high resistance undoped semiconducting base ( 53 ). This formation is useful as a energy conversion device due to the flow of gases ( 54 ) there across. The electrical signals obtained are first harnessed and then measured using a voltmeter/ammeter ( 55 ). The sensing elements and the metal connecting wires can be fabricated on a single chip.
  • one embodiment is to take advantage of inverse Seebeck coefficients of n and p type Si or Ge. This embodiment is depicted in FIG. 6 wherein the n and p type semiconducting strips ( 61 ) are alternated. The n and p type semiconducting strips are made by ion implantation. Strips of undoped semiconducting material ( 62 ) are sandwiched between n and p type semiconducting strips ( 61 ).
  • n and p type semiconducting strips ( 61 ) are electrically bonded in series through a conducting material ( 63 ) to add the individual Seeback voltages when the sample is exposed to the gas flow ( 64 ).
  • the entire assembly is provided on a semiconducting base ( 65 ) and is connected to a voltmeterammeter ( 66 ).
  • Another significant advantage of the flow sensor device of the invention is that it does not require any external power source for operation. On the contrary, the device of the invention generates electricity. The movement of the gas across the solid material results in the generation of a current I. The material along with the contacts have a resistance R, thereby enabling the formation of a voltage V across the sensor.
  • FIG. 1( d ) shows a schematic layout of the experimental set up used in example 1 to achieve a calibrated gas flow velocity in the flow sensing device of the invention.
  • Flow sensing devices comprising 3 ⁇ 10 ⁇ 3 m along the gas flow and 1 ⁇ 10 ⁇ 3 m perpendicular to the gas flow were used.
  • the electrical contacts comprised of copper leads of 125 ⁇ 10 ⁇ 6 m diameter made using silver emulsion (shown in the shaded region in FIG. 1( b )).
  • the exposed area of the flow sensor element is not covered by the silver emulsion and was about 2 ⁇ 10 ⁇ 3 m along the flow and 1 ⁇ 10 ⁇ 3 m perpendicular to the flow of the gas.
  • the sensing elements comprising single wall carbon nanotubes, multi-wall carbon nanotubes, and graphite were prepared by densely packing the powder between the two electrodes.
  • the dimensions of the active solid material were about 1 ⁇ 10 ⁇ 3 m along the flow, 2 ⁇ 10 ⁇ 3 m wide and 2 ⁇ 10 ⁇ 4 nm thick.
  • FIG. 2 The results of nitrogen flow over p-Si, n-Si, n-Ge, SWNT, MWNT and graphite are depicted in FIG. 2 .
  • the voltage V varies as u 2 over a wide range of u as does current, which is not shown therein.
  • the gas is not compressible, it can be scaled by thermal speed (which is sound velocity) to give a plot of V versus the square of the Mach number M as depicted in FIG. 3 .
  • Example 2 The same set up as in Example 1 was repeated except that the flow sensor element was kept at a distance of 2 ⁇ 10 ⁇ 2 m from the exit point or 1 ⁇ 10 ⁇ 2 m outside the tube. The results obtained were similar to those in Example 1.
  • Example 1 The same experiment was repeated as in Example 1 except that the material in question was a solid polycrystalline copper sheet for which the slope of A was very small. The results are given in Table 1.
  • the method of the invention was tested using two separate gases, nitrogen and argon in order to measure the voltages V generated over large values of M 2 over n-Ge.
  • the results are shown in FIG. 4 .
  • the inset in FIG. 4 dearly shows that the slope A for M 2 ⁇ 0.05 (hereinafter referred to regime I) is higher for argon (solid squares in FIG. 4 ) as compared to that for nitrogen (open circles in FIG. 4 ).
  • the ratio of the slopes A(argon)/A(nitrogen) 1.2. It was established that there are two M 2 regimes by analysis of the mechanism behind the generation of electrical signal induced by the flow of gases over the solids.
  • the values for argon and nitrogen are 1.667 and 1.404 respectively.
  • P o is the maximum pressure at a point on the streamline where the velocity is zero. Such a point is the leading edge on the surface of the flow sensor element past which the gas is flowing and is called the stagnation point.
  • the pressure difference between the two ends of the sample exposed to the gas flow (without the electrodes) is given below in Equation 2.
  • Th subscripts L and R in equation 2 denote the left and right of the active part of the device when the gas flows from left to right.
  • the gas flowing past the flow sensing element is kept at an angle of ⁇ with respect to the horizontal axis corresponding to the accelerating flow and therefore M R >M L .
  • the tangential component of the velocity of the outer flow u depends on the streamline distance x measured along the flat boundary as given in Equation 4 below. u ⁇ ⁇ /( ⁇ ) . (4)
  • V k 2 ⁇ T 0 ⁇ S ⁇ ⁇ ⁇ ⁇ ( M R 2 - M L 2 ) .
  • S is the Seebeck coefficient of the solid and is positive for p-type since majority and negative for n-type materials.
  • Factor k depends on the specific interactions between the gas and the solid surface as well as the boundary conditions of the temperature difference between the solid and the gas.

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US20060042947A1 (en) * 2004-08-30 2006-03-02 Lockheed Martin Corporation Nanotube fluid pump
US20110240150A1 (en) * 2008-07-08 2011-10-06 Albemarle Corporation System and method for detecting pluggage in a conduit for delivery of solids and carrier gases to a flowing gas stream
RU2763208C1 (ru) * 2021-03-29 2021-12-28 Федеральное государственное бюджетное военное образовательное учреждение высшего образования "Военно-космическая академия имени А.Ф. Можайского" Министерства обороны Российской Федерации Способ контроля герметичности корпуса космического аппарата

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CN102338809A (zh) * 2011-06-21 2012-02-01 南京航空航天大学 一种基于石墨烯的气流生电或流速测定的方法及装置
US10016632B2 (en) * 2013-12-20 2018-07-10 B/E Aerospace, Inc. Oxygen flow indicator using flow-powered illumination
US10967205B2 (en) * 2013-12-20 2021-04-06 B/E Aerospace, Inc. Oxygen flow indicator using flow-powered illumination
US20170276527A1 (en) * 2016-03-25 2017-09-28 General Electric Company System and method for metering gas
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US7625475B2 (en) * 2004-08-30 2009-12-01 Lockheed Martin Corporation Nanotube fluid pump
US20110240150A1 (en) * 2008-07-08 2011-10-06 Albemarle Corporation System and method for detecting pluggage in a conduit for delivery of solids and carrier gases to a flowing gas stream
US8695446B2 (en) * 2008-07-08 2014-04-15 Albemarle Corporation System and method for detecting pluggage in a conduit for delivery of solids and carrier gases to a flowing gas stream
RU2763208C1 (ru) * 2021-03-29 2021-12-28 Федеральное государственное бюджетное военное образовательное учреждение высшего образования "Военно-космическая академия имени А.Ф. Можайского" Министерства обороны Российской Федерации Способ контроля герметичности корпуса космического аппарата

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